1. Field of the Invention
The present invention relates to a method and apparatus for machining a substrate such as, for example, a semiconductor wafer.
2. Description of the Related Art
In the field of manufacturing semiconductors, the dicing process for cutting a substrate such as, for example, a silicon wafer on which a plurality of semiconductor elements are formed, into cubic portions, i.e., dicing a substrate, is necessary. A substrate machining apparatus for dicing contains a disk-like blade. Before a dicing process, an adhesive dicing tape is attached to a wafer. After that, the blade is rotated to cut the wafer from its surface, on which no dicing tape is attached, while cutting water is supplied to the wafer. The blade is moved forward to form a street. Usually, only the wafer is cut without completely cutting the dicing tape. Streets are formed on the wafer in longitudinal and lateral directions so that a plurality of cubic dice are formed on the dicing tape. This is disclosed in, for example, FIG. 6 of Japanese Unexamined Patent Publication (Kokai) No. 2002-75919.
However, in the substrate machining method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2002-75919, there is a possibility that some problem may occur on a cut surface of the wafer. FIG. 4 is an enlarged sectional view of a diced substrate in a prior art. FIG. 5 is a partial perspective view of a diced substrate in a prior art. As shown in FIG. 4, chippings 910, 920 are formed on cut surfaces 210, 220 of a wafer 200, respectively, after a dicing operation, in the vicinity of lower edges of the cut surfaces 210, 220, i.e., in the vicinity of a dicing tape 300. As shown in FIG. 4, the chippings 910, 920 are also formed on the portion of the wafer 200 adjacent to the dicing tape 300, i.e., the bottom of the wafer 200. As shown in FIG. 5, such chippings 900 exist on the sides of chips or dice to be formed. Accordingly, cracks sometimes grow on the bottoms of chips or dice, so that the chips or dice are broken or become difficult to assemble, when stresses are applied to the chips or dice in picking-up and assembling operations of the chips or dice. Crushed layers, i.e., brittle fracture layers 810, 820 are formed in the cut surfaces 210, 220, along the thickness direction of the wafer 200. Likewise, there is a possibility that cracks may grow in the brittle fracture layers 810, 820 of the cut surfaces 210, 220 to break the chips or dice when stresses are applied to the chips or dice in picking-up and assembling operations of the chips or dice.
In view of the above problems, the object of the present invention is to provide a method and apparatus for machining a substrate which prevents chips and prevents dice from being broken in picking-up and assembling operations of the dice.